Acceleration slip regulation method and device for four-wheel drive electric vehicle

ABSTRACT

An acceleration slip regulation method and device for a four-wheel drive electric vehicle are disclosed. The method comprises the following steps: detecting wheel speeds of four wheels of an electric vehicle and a depth of depression of an accelerator pedal; estimating a vehicle speed of the electric vehicle according to the wheel speeds of the four wheels, determining a road condition at the location of the electric vehicle according to the wheel speeds of the four wheels and the vehicle speed, and acquiring a required torque of the electric vehicle according to the depth of depression of the accelerator pedal, wherein the road condition comprising a low adhesion starting road, a joint road, and a bisectional road; and performing acceleration slip regulation on the four wheels respectively according to the road condition and the required torque. The control method can ensure that the wheels do not slip, the electric vehicle does not undergo lateral displacement and a yaw rate is kept within a certain range after the electric vehicle activates acceleration slip. The control method can maximize the use of ground adhesion to improve the escape capability of the electric vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is proposed based on Chinese Patent Application No.201611251605.3, filed on Dec. 29, 2016, entitled “Acceleration SlipRegulation Method and Device for Four-Wheel Drive Electric Vehicle”, andclaims priority to the Chinese Patent Application, which is incorporatedherein by reference in its entirety.

FIELD

The present application relates to the technical field of electricvehicles and, in particular, to an acceleration slip regulation methodfor a four-wheel drive electric vehicle and an acceleration slipregulation device for a four-wheel drive electric vehicle.

BACKGROUND

In the related art, an acceleration slip regulation method for afour-wheel hub electric vehicle is proposed. Specifically, an optimalslip ratio of a wheel is calculated in real time by a road recognitionalgorithm, and a desired rotational speed of the wheel is calculatedfrom the optimal slip ratio of the wheel. Then, according to the stateof the wheel, a compensation torque of the wheel is calculated; if thewheel is slipping, a desired wheel speed is taken as a control target,and the compensation torque is calculated by a PID controller of thewheel speed; and if the wheel does not slip, the compensation torque iszero. Moreover, during vehicle speed control, a desired vehicle speed istaken as a control target, and a command torque of a motor is calculatedaccording to a vehicle speed controller. Finally, the compensationtorque and the command torque described above are added and input intothe motor to achieve acceleration slip regulation for the four-wheel hubelectric vehicle.

However, although the above technology mentions that the compensationtorque of the motor is calculated according to the road recognition andthe PID controller, it does not give an indication of how each wheelacts to make the vehicle not destabilize when the vehicle runs ondifferent roads. Because the four motor torques of the four-wheel hubelectric vehicle are controlled separately without affecting each other,if the vehicle runs on a bisectional road (i.e., only one wheel islocated on a low adhesion road, same-side wheels are located on a lowadhesion road and diagonal wheels are located on a low adhesion road),acceleration slip is triggered, and the vehicle may destabilize.

SUMMARY

An objective of the present application is to at least resolve one ofthe technical problems in the related art to some extent.

In view of this, the present invention is directed to an accelerationslip regulation method for a four-wheel drive electric vehicle. Thecontrol method can ensure that wheels do not slip, the electric vehicledoes not undergo lateral displacement and a yaw rate is kept within acertain range after an electric vehicle activates acceleration slip. Thecontrol method can maximize the use of ground adhesion to improve theescape capability of the electric vehicle.

The present invention is also directed to an acceleration slipregulation device for a four-wheel drive electric vehicle.

To achieve the above objectives, a first aspect embodiment of thepresent application provides an acceleration slip regulation method fora four-wheel drive electric vehicle. The method includes the followingsteps: detecting wheel speeds of four wheels of an electric vehicle anda depth of depression of an accelerator pedal; estimating a vehiclespeed of the electric vehicle according to the wheel speeds of the fourwheels, determining a road condition at the location of the electricvehicle according to the wheel speeds of the four wheels and the vehiclespeed, and acquiring a required torque of the electric vehicle accordingto the depth of depression of the accelerator pedal, the road conditionincluding a low adhesion starting road, a joint road, and a bisectionalroad; and performing acceleration slip regulation on the four wheelsrespectively according to the road condition and the required torque.

According to the acceleration slip regulation method for a four-wheeldrive electric vehicle of the embodiment of the present invention, aroad condition at the location of an electric vehicle is determinedaccording to wheel speeds of four wheels of the electric vehicle and avehicle speed, and a corresponding control strategy is taken accordingto the road condition to perform acceleration slip regulation on theelectric vehicle. Thus, it can be ensured that wheels do not slip, theelectric vehicle does not undergo lateral displacement and a yaw rate iskept within a certain range after an electric vehicle activatesacceleration slip, and the use of ground adhesion can be maximized toimprove the escape capability of the electric vehicle.

To achieve the above objectives, a second aspect embodiment of thepresent application provides an acceleration slip regulation device fora four-wheel drive electric vehicle. The device includes: a detectionmodule, adapted to detect wheel speeds of four wheels of the electricvehicle and a depth of depression of an accelerator pedal; an estimationmodule, adapted to estimate a vehicle speed of the electric vehicleaccording to the wheel speeds of the four wheels; a determinationmodule, adapted to determine a road condition at the location of theelectric vehicle according to the wheel speeds of the four wheels andthe vehicle speed, the road condition including a low adhesion startingroad, a joint road, and a bisectional road; an acquisition module,adapted to acquire a required torque of the electric vehicle accordingto the depth of depression of the accelerator pedal; and a controlmodule, connected to the determination module and the acquisition moduleseparately and adapted to perform acceleration slip regulation on thefour wheels respectively according to the road condition and therequired torque.

According to the acceleration slip regulation device for a four-wheeldrive electric vehicle of the embodiment of the present invention, aroad condition at the location of an electric vehicle is determinedaccording to wheel speeds of four wheels of the electric vehicle and avehicle speed, and a corresponding control strategy is taken accordingto the road condition to perform acceleration slip regulation on theelectric vehicle. Thus, it can be ensured that wheels do not slip, theelectric vehicle does not undergo lateral displacement and a yaw rate iskept within a certain range after an electric vehicle activatesacceleration slip, and the use of ground adhesion can be maximized toimprove the escape capability of the electric vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of embodiments of the presentinvention will become apparent and more readily appreciated from thefollowing descriptions made with reference to the drawings, in which:

FIG. 1 is a flowchart of an acceleration slip regulation method for afour-wheel drive electric vehicle according to an embodiment of thepresent invention;

FIG. 2a to FIG. 2g are respective diagrams of a road condition at thelocation of an electric vehicle according to specific embodiments of thepresent invention;

FIG. 3 is a curve chart of real vehicle test data of an electric vehiclefrom a low adhesion road to a high adhesion road according to anembodiment of the present invention;

FIG. 4 is a curve chart of real vehicle test data of an electric vehiclefrom a high adhesion road to a low adhesion road according to anembodiment of the present invention;

FIG. 5 is a curve chart of real vehicle test data of an electric vehicleon a bisectional road according to an embodiment of the presentinvention;

FIG. 6 is a flowchart of an acceleration slip regulation method for afour-wheel drive electric vehicle according to another embodiment of thepresent invention;

FIG. 7 is a principle schematic diagram of an acceleration slipregulation method for a four-wheel drive electric vehicle according toanother embodiment of the present invention;

FIG. 8a and FIG. 8b are respective curve charts of a joint simulation ofCarsim and Simulink when acceleration slip is not activated andacceleration slip is activated according to another embodiment of thepresent invention;

FIG. 9 is a curve chart of a real vehicle matching test on accelerationslip regulation for a four-wheel drive electric vehicle according toanother embodiment of the present invention; and

FIG. 10 is a structure block diagram of an acceleration slip regulationdevice for a four-wheel drive electric vehicle according to anembodiment of the present invention.

DETAILED DESCRIPTION

The following describes in detail embodiments of the present invention.Examples of the embodiments are shown in the accompanying drawings,where reference signs that are the same or similar may represent same orsimilar components or components that have same or similar functions.The following embodiments described with reference to the accompanyingdrawings are exemplary, and are intended to describe the presentinvention and cannot be construed as a limitation to the presentinvention.

An acceleration slip regulation method for a four-wheel drive electricvehicle and an acceleration slip regulation device for a four-wheeldrive electric vehicle according to an embodiment of the presentinvention are described below with reference to the accompanyingdrawings.

FIG. 1 is a flowchart of an acceleration slip regulation method for afour-wheel drive electric vehicle according to an embodiment of thepresent invention. As shown in FIG. 1, the method includes the followingsteps:

S1: Detect wheel speeds of four wheels of an electric vehicle and adepth of depression of an accelerator pedal.

In the embodiment of the present invention, the wheel speed of eachwheel of the electric vehicle can be detected by a wheel speed sensormounted on each wheel of the electric vehicle, and the depth ofdepression of the accelerator pedal can be detected by a displacementsensor mounted on the accelerator pedal. The wheel speed sensor may be,but is not limited to, a magneto-electric wheel speed sensor, a Halltype wheel speed sensor, etc.

S2: Estimate a vehicle speed of the electric vehicle according to thewheel speeds of the four wheels, determine a road condition at thelocation of the electric vehicle according to the wheel speeds of thefour wheels and the vehicle speed, and acquire a required torque of theelectric vehicle according to the depth of depression of the acceleratorpedal.

Specifically, when estimating the vehicle speed of the electric vehicleaccording to on the wheel speed, the following methods may be employed:(1) a minimum wheel speed method, where when the electric vehicleperforms acceleration slip regulation during driving, since the wheelslips and the wheel speed is greater than the vehicle speed, the minimumwheel speed of the four wheels may be taken as the vehicle speed; (2) aslope method, where through the analysis and processing of a largenumber of experimental data, an average acceleration achievable by theelectric vehicle on various roads is determined, based on this, in theprocess of acceleration slip regulation, an initial vehicle speedentering the acceleration slip regulation is determined, after a roadcondition and an acceleration slip operation condition are recognized,the acceleration of the electric vehicle is determined, and a speedvalue is calculated in real time according to a speed formula as areference vehicle speed; and (3) a determination method based on avehicle braking mechanical model, where the method can correct areference vehicle speed in real time on the basis of a model such as anentire vehicle and a tire, and can better simulate a real vehicle speed.It will be appreciated that the method for estimating a vehicle speed inthe embodiment of the present invention is not limited to the abovethree types.

In the embodiment of the present invention, the road condition includesa low adhesion starting road, a joint road, and a bisectional road.

The road condition of the joint road includes entering a high adhesionroad from a low adhesion road and entering a low adhesion road from ahigh adhesion road. The road condition of the bisectional road includesthat only one wheel is located on a low adhesion road, same-side wheelsare located on a low adhesion road, diagonal wheels are located on a lowadhesion road and three wheels are located on a low adhesion road.

Further, in an embodiment of the present invention, determining a roadcondition at the location of the electric vehicle according to the wheelspeeds of the four wheels and the vehicle speed specifically includes:judging whether the wheel speeds of the four wheels are greater than thevehicle speed, respectively; determining, if the wheel speeds of thefour wheels are all greater than the vehicle speed, that the roadcondition is the low adhesion starting road; determining, if the wheelspeeds of front wheels of the electric vehicle are both equal to thevehicle speed and the wheel speeds of rear wheels are both greater thanthe vehicle speed, that the road condition is the joint road and theelectric vehicle enters a high adhesion road from a low adhesion road;determining, if the wheel speeds of the front wheels are both greaterthan the vehicle speed and the wheel speeds of the rear wheels are bothequal to the vehicle speed, that the road condition is the joint roadand the electric vehicle enters a low adhesion road from a high adhesionroad; determining, if the wheel speed of only one wheel is greater thanthe vehicle speed and the wheel speeds of the other three wheels are allequal to the vehicle speed, that the road condition is the bisectionalroad and the single wheel is located on a low adhesion road;determining, if the wheel speed of one same-side wheel is greater thanthe vehicle speed and the wheel speed of the other same-side wheel isequal to the vehicle speed, that the road condition is the bisectionalroad and one same-side wheel is located on a low adhesion road;determining, if the wheel speed of one diagonal wheel is greater thanthe vehicle speed and the wheel speed of the other diagonal wheel isequal to the vehicle speed, that the road condition is the bisectionalroad and one diagonal wheel is located on a low adhesion road; anddetermining, if the wheel speeds of three wheels are greater than thevehicle speed and the wheel speed of the other wheel is equal to thevehicle speed, that the road condition is the bisectional road and thethree wheels are located on a low adhesion road.

S3: Perform acceleration slip regulation on the four wheels respectivelyaccording to the road condition and the required torque.

In an embodiment of the present invention, if the road condition is thelow adhesion starting road, the four wheels of the electric vehicle arecontrolled to activate acceleration slip, each wheel being separatelycontrolled by a corresponding motor.

Specifically, as shown in FIG. 2a , if the wheel speeds of the fourwheels of the electric vehicle are all greater than the vehicle speed,the four wheels simultaneously slip, that is, the electric vehicle runson the low adhesion starting road. At this time, the four wheels arecontrolled to activate acceleration slip, and each wheel is separatelycontrolled by the corresponding motor without affecting each other.

In another embodiment of the present invention, as shown in FIG. 2b , ifthe electric vehicle enters a high adhesion road from a low adhesionroad, an integral coefficient in a PI controller corresponding to amotor of a front wheel is increased respectively to increase anacceleration slip torque of the front wheel, and the front wheel iscontrolled to exit the acceleration slip when the acceleration sliptorque is greater than or equal to the required torque.

Specifically, as shown in FIG. 3, when the electric vehicle runs on thelow adhesion road, the four wheels all activate the acceleration slip,the wheel speeds are greater than the vehicle speed, and the wheelspeeds are equal to the vehicle speed after entering the high adhesionroad. At this time, the integral coefficient in the PI controllercorresponding to the motor of the front wheel is increased respectively,so the corresponding acceleration slip torque will be quickly increased.When the acceleration slip torque is equal to the required torque, thefront wheel is controlled to exit the acceleration slip.

It will be appreciated that there will be a short-time situation wherethe front wheel enters the high adhesion road while the rear wheel isstill on the low adhesion road during this process. At this time, thefront wheel is processed according to the above strategy, the rear wheelis still in an acceleration slip activating state, and after the rearwheel enters the high adhesion road, the rear wheel is also processedaccording to the above strategy, where the front and rear wheels areprocessed separately and do not affect each other.

Correspondingly, as shown in FIG. 2c , if the electric vehicle entersthe low adhesion road from the high adhesion road, the front wheel iscontrolled to activate the acceleration slip, and torque decrease isperformed on the motor of the front wheel to prevent the front wheelfrom slipping.

Specifically, as shown in FIG. 4, when the wheel enters the highadhesion road from the low adhesion road, if a driver depresses theaccelerator pedal deeply and a road adhesion coefficient is small, thewheel may suddenly slip. At this time, the front wheel is controlled toimmediately activate the acceleration slip to reduce a drive torque forthe motor of the front wheel, so that the front wheel does not slip orslips briefly, the rear wheel is not processed when it does not enterthe low adhesion road, and the acceleration slip is activated after therear wheel also enters the low adhesion road.

In yet another embodiment of the present invention, as shown in FIG. 2d, if only one wheel is located on the low adhesion road, whether thevehicle speed is less than a preset vehicle speed is judged; if thevehicle speed is less than the preset vehicle speed, the wheel on thelow adhesion road is controlled to activate acceleration slip; and ifthe vehicle speed is greater than or equal to the preset vehicle speed,torque limiting is performed on a motor of a wheel on the high adhesionroad, which is coaxial with the wheel on the low adhesion road, so as toprevent the electric vehicle from lateral displacement, a drive torquefor the motor of the wheel on the high adhesion road, which is coaxialwith the wheel on the low adhesion road, being equal to a sum of a drivetorque for a motor of the wheel on the low adhesion road and a presettorque limit difference.

In the embodiment of the present invention, the preset torque limitdifference may be derived by simulation and real vehicle matching.

Specifically, if the vehicle speed is low, it can be regarded as theelectric vehicle escaping or running at a low speed. At this time, onlythe wheel on the low adhesion road is controlled to activateacceleration slip while the other wheels are not processed, that is, thedrive torques for motors of the other wheels are the required torque. Ifthe vehicle speed is high, it is necessary to perform appropriate torquelimiting on the motor of the wheel on the high adhesion road, which iscoaxial with a slipping wheel (that is, the wheel on the low adhesionroad), so that the electric vehicle is prevented from lateraldisplacement. The torque limit method is: obtaining the drive torque forthe motor of the wheel on the high adhesion road, which is coaxial withthe slipping wheel by adding the drive torque for the motor of the wheelon the low adhesion road to the preset torque limit difference.

In a fourth embodiment of the present invention, as shown in FIG. 2e ,if same-side wheels are located on the low adhesion road, the wheels onthe low adhesion road are controlled to activate acceleration slip, andtorque limiting is performed on wheels on the high adhesion road, so asto prevent the electric vehicle from lateral displacement, a drivetorque for motors of the wheels on the high adhesion road being equal toa sum of a motor torque for motors of the corresponding wheels on thelow adhesion road and a preset torque limit difference.

In a fifth embodiment of the present invention, as shown in FIG. 2f , ifdiagonal wheels are located on the low adhesion road, the diagonalwheels on the low adhesion road are controlled to activate accelerationslip, and torque decrease is performed on motors of the diagonal wheelson the low adhesion road.

Specifically, if one diagonal wheel is located on the low adhesion road,the diagonal wheel on the low adhesion road is controlled to activateacceleration slip, so that a motor undergoes torque decrease. The otherdiagonal wheel on the high adhesion road does not activate accelerationslip, and the corresponding motor does not perform torque limiting, anddirectly responds to the required torque. It will be appreciated thatthe electric vehicle is prevented from lateral displacement at thistime.

In a sixth embodiment of the present invention, as shown in FIG. 2g , ifthree wheels are located on the low adhesion road, the three wheels onthe low adhesion road are controlled to activate acceleration slip, andwhether the vehicle speed is less than a preset vehicle speed is judged;if the vehicle speed is less than the preset vehicle speed, a drivetorque for a motor of a wheel on the high adhesion road is controlled tobe the required torque; and if the vehicle speed is greater than orequal to the preset vehicle speed, torque limiting is performed on themotor of the wheel on the high adhesion road, so as to prevent theelectric vehicle from lateral displacement, the drive torque for themotor of the wheel on the high adhesion road being equal to a sum of adrive torque for a motor of a wheel, which is located on the lowadhesion road and coaxial with the wheel on the high adhesion road, anda preset torque limit difference.

Specifically, if three wheels are located on the low adhesion road, thethree wheels on the low adhesion road are controlled to activateacceleration slip. If the vehicle speed is low, it can be regarded asthe electric vehicle running at a low speed or escaping, and the motoron the high adhesion road responds to the required torque. If thevehicle speed is high, it is possible to perform appropriate torquelimiting on the motor of the wheel on the high adhesion road in order toprevent the electric vehicle from lateral displacement. The torque limitmethod is: obtaining the drive torque for the motor of the wheel on thehigh adhesion road by adding the drive torque for the motor of thewheel, which is located on the low adhesion road and coaxial with thewheel on the high adhesion road to the preset torque limit difference.

Specifically, as shown in FIG. 5, when the road condition at thelocation of the electric vehicle is the bisectional road, the drivetorque for the motor of the wheel on the high adhesion road and thedrive torque for the motor of the wheel on the low adhesion road keep anappropriate torque difference, so that the vehicle does not undergolateral displacement.

According to the acceleration slip regulation method for a four-wheeldrive electric vehicle of the embodiment of the present invention, aroad condition at the location of an electric vehicle is determinedaccording to wheel speeds of four wheels of the electric vehicle and avehicle speed, and a corresponding control strategy is taken accordingto the road condition to perform acceleration slip regulation on theelectric vehicle. Thus, it can be ensured that wheels do not slip, theelectric vehicle does not undergo lateral displacement and a yaw rate iskept within a certain range after an electric vehicle activatesacceleration slip, and the use of ground adhesion can be maximized toimprove the escape capability of the electric vehicle.

In addition, it is to be noted that, for the wheel on the low adhesionroad in the above embodiment, in order to keep a suitable slip ratio, inan embodiment of the present invention, as shown in FIG. 6, step S2further includes: determining, according to the vehicle speed, a targetdifference between the vehicle speed and the wheel speed.

In the embodiment of the present invention, a corresponding relationshipexists between the vehicle speed and the target difference. When thevehicle speed is greater than 10 km/h, the corresponding targetdifference ranges from 1.5 km/h to 2 km/h. For example, if the vehiclespeed is 15 km/h, the corresponding target difference is 2 km/h.

Specifically, a target difference Dv_aim is not fixed and varies alongwith the change of the vehicle speed. When the vehicle speed is low, thetarget difference Dv_aim is large, and when the vehicle speed is high,the target difference Dv_aim is small.

Further, as shown in FIG. 6, step S3 further includes: performingacceleration slip regulation on the wheel corresponding to the wheelspeed according to the wheel speed, the vehicle speed, the targetdifference and the required torque.

Specifically, if the difference between the wheel speed and the vehiclespeed is greater than the target difference, a PI controller foracceleration slip regulation corresponding to the motor of the wheel iscorrected according to the wheel speed, the vehicle speed and the targetdifference, so as to output a corresponding acceleration slip torquethrough the corrected PI controller; whether the acceleration sliptorque is less than the required torque is judged; if the accelerationslip torque is less than the required torque, it is determined that thedrive torque for the motor of the wheel is the acceleration slip torque;and if the acceleration slip torque is greater than or equal to therequired torque, it is determined that the drive torque for the motor ofthe wheel is the required torque and the wheel is controlled to exitacceleration slip.

In the embodiment of the present invention, the PI controller foracceleration slip regulation corresponding to the motor of the wheelintroduces, on the basis of the conventional classical PI control, afeedback amount (Dvx−Dv_aim) to correct a proportional coefficient P andan integral coefficient I, where Dvx is a difference between the wheelspeed and the vehicle speed, and Dv_aim is a target differencecorresponding to a current vehicle speed.

Specifically, the integral coefficient I of the PI controller iscorrected according to the difference Dvx between the wheel speed andthe vehicle speed and the target difference Dv_aim, and the proportionalcoefficient of the PI controller is kept unchanged; and further, adifference between the difference Dvx and the target difference Dv_aimis used as a feedback value of the PI controller, and the correspondingacceleration slip torque T_value is output.

The appropriate value of the proportional coefficient P may be unchangedby simulation and real vehicle debugging, and the integral coefficient Iof the corrected PI controller is positively proportional to an absolutevalue of (Dvx−Dv_aim). That is, as the absolute value is larger, theintegral coefficient is larger; as the absolute value is smaller, theintegral coefficient is smaller; and when the absolute value is 0, theintegral coefficient is 0.

Specifically, (Dvx−Dv_aim) is used as feedback and is multiplied by theproportional coefficient to obtain a proportional term P_value;meanwhile, a product of (Dvx−Dv_aim) and the integral coefficient isintegrated to obtain an integral term I_value; and then the proportionalterm and the integral term are added together to obtain the accelerationslip torque T_value. If the calculated T_value is less than 0, it islimited to 0, that is, the acceleration slip process does not give anegative drive torque to the motor of the wheel.

In order to facilitate understanding of the above acceleration slipregulation method for a single wheel, it can be illustrated by FIG. 7,FIG. 8a , FIG. 8b , and FIG. 9:

As shown in FIG. 7, an accelerator signal is inputted through anaccelerator pedal of an electric vehicle, and a required torque of theelectric vehicle is acquired according to the accelerator signal. Wheelspeeds of four wheels of the electric vehicle are detected by wheelspeed sensors, and a vehicle speed of the electric vehicle may beestimated according to the speeds of four wheels. Whether the wheelspeed of each wheel is greater than the vehicle speed is judged, thewheel of which the wheel speed is greater than the vehicle speed iscontrolled to activate acceleration slip regulation, a target differenceDv_aim between the vehicle speed and the wheel speed is then acquiredaccording to the vehicle speed, and a difference Dvx between the wheelspeed of the wheel and the vehicle speed may be calculated.

Further, when Dvx is greater than Dv_aim, a difference (that is,Dvx−Dv_aim) between the difference Dvx and the target difference Dv_aimis calculated, and a proportional coefficient P and an integralcoefficient I of a PI controller for acceleration slip regulationcorresponding to a motor of the wheel are corrected according to thedifference. The proportional coefficient P may be kept unchanged at acertain value by simulation and real vehicle debugging, and the integralcoefficient I is positively proportional to an absolute value of(Dvx−Dv_aim). That is, as the absolute value is larger, the correctedintegral coefficient is larger; as the absolute value is smaller, theintegral coefficient is smaller; and when the absolute value is 0, theintegral coefficient is 0. Further, an acceleration slip torque isoutputted according to the corrected PI controller, when theacceleration slip torque is less than the required torque, the drivetorque for the motor of the wheel is taken as the acceleration sliptorque, and when the acceleration slip torque is greater than or equalto the required torque, the drive torque for the motor of the wheel istaken as the required torque and the electric vehicle is controlled toexit acceleration slip. Therefore, the wheel of the electric vehicle maybe stabilized under the acceleration slip, an appropriate slip ratio iskept, and the ground driving force of the wheel is increased.

As shown in FIG. 8a , when a driver slams an accelerator on the lowadhesion road and the wheel does not activate acceleration slip, thewheel speed of the slipping wheel will rise rapidly to the maximum speedof the motor of the wheel, and cannot be stabilized. As shown in FIG. 8b, after the acceleration slip is activated, the wheel may be controlledby the PI controller with a slight slip, so that the wheel speed isgradually stabilized.

As shown in FIG. 9, in a real vehicle test, the test condition isfull-accelerator starting on the low adhesion road, and meanwhile, thecomfort of the driver and passengers is taken into consideration. It canbe seen from FIG. 9 that the above acceleration slip regulation has abetter regulation effect and a good real vehicle experience.

In summary, according to the acceleration slip regulation method for afour-wheel drive electric vehicle, the road condition at the location ofthe electric vehicle is determined according to the wheel speeds of thefour wheels of the electric vehicle and the vehicle speed, accelerationslip regulation is performed on the electric vehicle by taking acorresponding control strategy according to the road condition, and forthe wheel activating acceleration slip regulation, when the differencebetween the wheel speed and the vehicle speed exceeds a targetdifference, the drive torque for the motor of the wheel is subjected toPI adjustment by taking the difference between the wheel speed and thevehicle speed as a control target. Thus, it can be ensured that wheelsdo not slip, the electric vehicle does not undergo lateral displacementand a yaw rate is kept within a certain range after the electric vehicleactivates acceleration slip, and the use of ground adhesion can bemaximized, so that the difference between the wheel speed and thevehicle speed is stabilized within a corresponding target differencerange to keep an appropriate slip ratio, which helps to improve theescape capability of the electric vehicle.

FIG. 10 is a structure block diagram of an acceleration slip regulationdevice for a four-wheel drive electric vehicle according to anembodiment of the present invention. As shown in FIG. 10, the deviceincludes: a detection module 10, an estimation module 20, adetermination module 30, an acquisition module 40, and a control module50.

The detection module 10 is adapted to detect wheel speeds of four wheelsof an electric vehicle and a depth of depression of an acceleratorpedal. The estimation module 20 is adapted to estimate a vehicle speedof the electric vehicle according to the wheel speeds of the fourwheels. The determination module 30 is adapted to determine a roadcondition at the location of the electric vehicle according to the wheelspeeds of the four wheels and the vehicle speed, the road conditionincluding a low adhesion starting road, a joint road, and a bisectionalroad. The acquisition module 40 is adapted to acquire a required torqueof the electric vehicle according to the depth of depression of theaccelerator pedal. The control module 50 is connected to thedetermination module 30 and the acquisition module 40 separately, andthe control module 50 is adapted to perform acceleration slip regulationon the four wheels respectively according to the road condition and therequired torque.

In the embodiment of the present invention, the determination module 30is specifically adapted to: judge whether the wheel speeds of the fourwheels are greater than the vehicle speed, respectively; determine, whenthe wheel speeds of the four wheels are all greater than the vehiclespeed, that the road condition is the low adhesion starting road;determine, when the wheel speeds of front wheels of the electric vehicleare both equal to the vehicle speed and the wheel speeds of rear wheelsare both greater than the vehicle speed, that the road condition is thejoint road and the electric vehicle enters a high adhesion road from alow adhesion road; determine, when the wheel speeds of the front wheelsare both greater than the vehicle speed and the wheel speeds of the rearwheels are both equal to the vehicle speed, that the road condition isthe joint road and the electric vehicle enters a low adhesion road froma high adhesion road; determine, when the wheel speed of only one wheelis greater than the vehicle speed and the wheel speeds of the otherthree wheels are all equal to the vehicle speed, that the road conditionis the bisectional road and the single wheel is located on a lowadhesion road; determine, when the wheel speed of one same-side wheel isgreater than the vehicle speed and the wheel speed of the othersame-side wheel is equal to the vehicle speed, that the road conditionis the bisectional road and one same-side wheel is located on a lowadhesion road; determine, when the wheel speed of one diagonal wheel isgreater than the vehicle speed and the wheel speed of the other diagonalwheel is equal to the vehicle speed, that the road condition is thebisectional road and one diagonal wheel is located on a low adhesionroad; and determine, when the wheel speeds of three wheels are greaterthan the vehicle speed and the wheel speed of the other wheel is equalto the vehicle speed, that the road condition is the bisectional roadand the three wheels are located on a low adhesion road.

Further, in an embodiment of the present invention, as shown in FIG. 2a, the control module 50 is specifically adapted to: control, when theroad condition is the low adhesion starting road, the four wheels of theelectric vehicle to activate acceleration slip, each wheel beingseparately controlled by a corresponding motor.

In another embodiment of the present invention, as shown in FIG. 2b ,the control module 50 is further specifically adapted to: increase, whenthe electric vehicle enters a high adhesion road from a low adhesionroad, an integral coefficient in a PI controller corresponding to amotor of a front wheel respectively to increase an acceleration sliptorque of the motor of the front wheel, and control the front wheel toexit the acceleration slip when the acceleration slip torque is greaterthan or equal to the required torque. As shown in FIG. 2c , when theelectric vehicle enters the low adhesion road from the high adhesionroad, the front wheels are controlled to both activate the accelerationslip, and drive torques for motors of the front wheels are reducedrespectively to prevent the front wheels from slipping.

In yet another embodiment of the present invention, as shown in FIG. 2d, the control module 50 is further specifically adapted to: judge, whenonly one single wheel is located on a low adhesion road, whether thevehicle speed is less than a preset vehicle speed; control, when thevehicle speed is less than the preset vehicle speed, the wheel on thelow adhesion road to activate acceleration slip; and perform, when thevehicle speed is greater than or equal to the preset vehicle speed,torque limiting on a wheel on a high adhesion road, which is coaxialwith the wheel on the low adhesion road, so as to prevent the electricvehicle from lateral displacement, a drive torque for the motor of thewheel on the high adhesion road, which is coaxial with the wheel on thelow adhesion road, being equal to a sum of a drive torque for a motor ofthe wheel on the low adhesion road and a preset torque limit difference.

In an embodiment of the present invention, as shown in FIG. 2e , thecontrol module 50 is further specifically adapted to: control, when onesame-side wheel is located on a low adhesion road, the wheel on the lowadhesion road to activate acceleration slip, and perform torque limitingon a wheel on a high adhesion road, so as to prevent the electricvehicle from lateral displacement, a drive torque for the motor of thewheel on the high adhesion road being equal to a sum of a correspondingdrive torque for a motor of the coaxial wheel on the low adhesion roadand a preset torque limit difference.

In a fifth embodiment of the present invention, as shown in FIG. 2f ,the control module 50 is further specifically adapted to: control, whenone diagonal wheel is located on a low adhesion road, the diagonal wheelon the low adhesion road to activate acceleration slip, and performtorque decrease on a motor of the diagonal wheel on the low adhesionroad.

In a sixth embodiment of the present invention, the control module 50 isfurther specifically adapted to: control, when three wheels are locatedon a low adhesion road, the three wheels on the low adhesion road toactivate acceleration slip, and judge whether the vehicle speed is lessthan a preset vehicle speed; control, when the vehicle speed is lessthan the preset vehicle speed, a drive torque for a motor of a wheel ona high adhesion road to be the required torque; and perform, when thevehicle speed is greater than or equal to the preset vehicle speed,torque limiting on the motor of the wheel on the high adhesion road, soas to prevent the electric vehicle from lateral displacement, the drivetorque for the motor of the wheel on the high adhesion road being equalto a sum of a drive torque for a motor of a wheel, which is located onthe low adhesion road and coaxial with the wheel on the high adhesionroad, and a preset torque limit difference.

It is to be noted that the specific implementation manner of theacceleration slip regulation device for a four-wheel drive electricvehicle according to the embodiment of the present invention is the sameas the specific implementation manner of the acceleration slipregulation method for a four-wheel drive electric vehicle according tothe embodiment of the present invention. In order to reduce redundancy,there is no repeated description.

According to the acceleration slip regulation device for a four-wheeldrive electric vehicle of the embodiment of the present invention, aroad condition at the location of an electric vehicle is determinedaccording to wheel speeds of four wheels of the electric vehicle and avehicle speed, and a corresponding control strategy is taken accordingto the road condition to perform acceleration slip regulation on theelectric vehicle. Thus, it can be ensured that wheels do not slip, theelectric vehicle does not undergo lateral displacement and a yaw rate iskept within a certain range after an electric vehicle activatesacceleration slip, and the use of ground adhesion can be maximized toimprove the escape capability of the electric vehicle.

In addition, it is noted that, for the wheel on the low adhesion road inthe above embodiment, in order to keep a suitable slip ratio, in anembodiment of the present invention, the determination module 30 isfurther adapted to determine, according to the vehicle speed, a targetdifference between the vehicle speed and the wheel speed. The controlmodule 50 is further adapted to perform acceleration slip regulation onthe wheel corresponding to the wheel speed according to the wheel speed,the vehicle speed, the target difference and the required torque.

In the embodiment of the present invention, a corresponding relationshipexists between the vehicle speed and the target difference. When thevehicle speed is greater than 10 km/h, the corresponding targetdifference ranges from 1.5 km/h to 2 km/h. For example, if the vehiclespeed is 15 km/h, the corresponding target difference is 2 km/h.

Specifically, a target difference Dv_aim is not fixed and varies alongwith the change of the vehicle speed. When the vehicle speed is low, thetarget difference Dv_aim is large, and when the vehicle speed is high,the target difference Dv_aim is small.

In an embodiment of the present invention, the control module 50 isspecifically adapted to: correct, when the difference between the wheelspeed and the vehicle speed is greater than the target difference, a PIcontroller for acceleration slip regulation corresponding to the motorof the wheel according to the wheel speed, the vehicle speed and thetarget difference, so as to output a corresponding acceleration sliptorque through the corrected PI controller; judge whether theacceleration slip torque is less than the required torque; determine,when the acceleration slip torque is less than the required torque, thatthe drive torque for the motor of the wheel is the acceleration sliptorque; and determine, when the acceleration slip torque is greater thanor equal to the required torque, that the drive torque for the motor ofthe wheel is the required torque and the wheel is controlled to exitacceleration slip.

In an embodiment of the present invention, the PI controller introduces,on the basis of the conventional classical PI control, a feedback amountto correct a proportional coefficient P and an integral coefficient I.

Specifically, the control module 50 is specifically adapted to: correct,when correcting the PI controller for acceleration slip regulationcorresponding to the motor of the wheel according to the wheel speed,the vehicle speed and the target difference so as to output acorresponding acceleration slip torque through the corrected PIcontroller, the integral coefficient of the PI controller according tothe difference Dvx between the wheel speed and the vehicle speed and thetarget difference Dv_aim, and keep the proportional coefficient of thePI controller unchanged; and use a difference between the difference Dvxand the target difference Dv_aim as a feedback value of the PIcontroller, and output the corresponding acceleration slip torqueT_value.

The appropriate value of the proportional coefficient P may be unchangedby simulation and real vehicle debugging, and the integral coefficient Iof the corrected PI controller is positively proportional to an absolutevalue of (Dvx−Dv_aim). That is, as the absolute value is larger, theintegral coefficient is larger; as the absolute value is smaller, theintegral coefficient is smaller; and when the absolute value is 0, theintegral coefficient is 0.

Specifically, (Dvx−Dv_aim) used as feedback is multiplied by theproportional coefficient to obtain a proportional term P_value;meanwhile, a product of (Dvx−Dv_aim) and the integral coefficient isintegrated to obtain an integral term I_value; and then the proportionalterm and the integral term are added together to obtain the accelerationslip torque T_value. If the calculated T_Value is less than 0, it islimited to 0, that is, the acceleration slip process does not give anegative drive torque to the motor of the wheel.

It is to be noted that the specific implementation manner of theacceleration slip regulation device for a four-wheel drive electricvehicle according to this embodiment may refer to the specificimplementation manner of the acceleration slip regulation method for afour-wheel drive electric vehicle according to the above embodiment ofthe present invention. In order to reduce redundancy, there is norepeated description.

In summary, according to the acceleration slip regulation device for afour-wheel drive electric vehicle, the determination module determinesthe road condition at the location of the electric vehicle according tothe wheel speeds of the four wheels of the electric vehicle and thevehicle speed, the control module performs acceleration slip regulationon the electric vehicle by taking a corresponding control strategyaccording to the road condition, and for the wheel activatingacceleration slip regulation, when the difference between the wheelspeed and the vehicle speed exceeds a target difference, the controlmodule performs pi adjustment on the drive torque for the motor of thewheel by taking the difference between the wheel speed and the vehiclespeed as a control target. Thus, it can be ensured that wheels do notslip, the electric vehicle does not undergo lateral displacement and ayaw rate is kept within a certain range after the electric vehicleactivates acceleration slip, and the use of ground adhesion can bemaximized, so that the difference between the wheel speed and thevehicle speed is stabilized within a corresponding target differencerange to keep an appropriate slip ratio, which helps to improve theescape capability of the electric vehicle.

The foregoing embodiments are only exemplary embodiments of the presentinvention and are not to limit the present invention in any forms.Though the above embodiments are disclosed in the present invention, theembodiments are not to limit the present invention. Those skilled in theart can use the methods and technical contents disclosed above to makevarious possible variations and modifications to the technical solutionsof the present invention or make equivalent changes to obtain equivalentembodiments without departing from the scope of the technical solutionsof the present invention. Therefore, any simple changes, equivalentvariations, and modifications made to the above embodiments according tothe technical essence of the present invention without departing fromthe contents of the technical solutions of the present invention shallfall within the scope of the technical solutions of the presentinvention.

1. An acceleration slip regulation method for a four-wheel driveelectric vehicle, comprising: detecting wheel speeds of four wheels ofthe electric vehicle and a depth of depression of an accelerator pedal;estimating a vehicle speed of the electric vehicle according to thewheel speeds of the four wheels, determining a road condition at alocation of the electric vehicle according to the wheel speeds of thefour wheels and the vehicle speed, and acquiring a required torque ofthe electric vehicle according to the depth of depression of theaccelerator pedal, the road condition comprising a low adhesion startingroad, a joint road, and a bisectional road; and performing accelerationslip regulation on the four wheels respectively according to the roadcondition and the required torque.
 2. The acceleration slip regulationmethod for a four-wheel drive electric vehicle according to claim 1,wherein the determining a road condition at the location of the electricvehicle according to the wheel speeds of the four wheels and the vehiclespeed comprises: determining whether the wheel speeds of the four wheelsare greater than the vehicle speed, respectively; determining, when thewheel speeds of the four wheels are all greater than the vehicle speed,that the road condition is the low adhesion starting road; determining,when the wheel speeds of front wheels of the electric vehicle are bothequal to the vehicle speed and the wheel speeds of rear wheels are bothgreater than the vehicle speed, that the road condition is the jointroad and the electric vehicle enters a high adhesion road from a lowadhesion road; determining, when the wheel speeds of the front wheelsare both greater than the vehicle speed and the wheel speeds of the rearwheels are both equal to the vehicle speed, that the road condition isthe joint road and the electric vehicle enters a low adhesion road froma high adhesion road; determining, when the wheel speed of only onewheel is greater than the vehicle speed and the wheel speeds of theother three wheels are all equal to the vehicle speed, that the roadcondition is the bisectional road and the single wheel is located on alow adhesion road; determining, when the wheel speed of one same-sidewheel is greater than the vehicle speed and the wheel speed of the othersame-side wheel is equal to the vehicle speed, that the road conditionis the bisectional road and one same-side wheel is located on a lowadhesion road; determining, when the wheel speed of one diagonal wheelis greater than the vehicle speed and the wheel speed of the otherdiagonal wheel is equal to the vehicle speed, that the road condition isthe bisectional road and one diagonal wheel is located on a low adhesionroad; and determining, when the wheel speeds of three wheels are greaterthan the vehicle speed and the wheel speed of the other wheel is equalto the vehicle speed, that the road condition is the bisectional roadand the three wheels are located on a low adhesion road.
 3. Theacceleration slip regulation method for a four-wheel drive electricvehicle according to claim 1, wherein the step of performingacceleration slip regulation on the four wheels respectively accordingto the road condition and the required torque comprises: controlling,when the road condition is the low adhesion starting road, the fourwheels of the electric vehicle to activate acceleration slip, each wheelbeing separately controlled by a corresponding motor.
 4. Theacceleration slip regulation method for a four-wheel drive electricvehicle according to claim 1, wherein the step of performingacceleration slip regulation on the four wheels respectively accordingto the road condition and the required torque further comprises:increasing, when the electric vehicle enters a high adhesion road from alow adhesion road, an integral coefficient in a PI controllercorresponding to a motor of a front wheel respectively to increase anacceleration slip torque of the front wheel, and controlling the frontwheel to exit the acceleration slip when the acceleration slip torque isgreater than or equal to the required torque; and controlling, when theelectric vehicle enters a low adhesion road from a high adhesion road,the front wheel to activate the acceleration slip, and performing torquedecrease on the motor of the front wheel to prevent the front wheel fromslipping.
 5. The acceleration slip regulation method for a four-wheeldrive electric vehicle according to claim 1, wherein the step ofperforming acceleration slip regulation on the four wheels respectivelyaccording to the road condition and the required torque furthercomprises: determining, when a single wheel is located on a low adhesionroad, whether the vehicle speed is less than a preset vehicle speed;controlling, when the vehicle speed is less than the preset vehiclespeed, the wheel on the low adhesion road to activate acceleration slip;and performing, when the vehicle speed is greater than or equal to thepreset vehicle speed, torque limiting on a motor of a wheel on a highadhesion road, which is coaxial with the wheel on the low adhesion road,so as to prevent the electric vehicle from lateral displacement, a drivetorque for the motor of the wheel on the high adhesion road, which iscoaxial with the wheel on the low adhesion road, being equal to a sum ofa drive torque for a motor of the wheel on the low adhesion road and apreset torque limit difference.
 6. The acceleration slip regulationmethod for a four-wheel drive electric vehicle according to claim 1,wherein the step of performing acceleration slip regulation on the fourwheels respectively according to the road condition and the requiredtorque further comprises: controlling, when one same-side wheel islocated on a low adhesion road, the wheel on the low adhesion road toactivate acceleration slip, and performing torque limiting on a motor ofa wheel on a high adhesion road, so as to prevent the electric vehiclefrom lateral displacement, a drive torque for the motor of the wheel onthe high adhesion road being equal to a sum of a corresponding drivetorque for a motor of the wheel on the low adhesion road and a presettorque limit difference.
 7. The acceleration slip regulation method fora four-wheel drive electric vehicle according to claim 1, wherein thestep of performing acceleration slip regulation on the four wheelsrespectively according to the road condition and the required torquefurther comprises: controlling, when one diagonal wheel is located on alow adhesion road, the diagonal wheel on the low adhesion road toactivate acceleration slip, and performing torque decrease on a motor ofthe diagonal wheel on the low adhesion road.
 8. The acceleration slipregulation method for a four-wheel drive electric vehicle according toclaim 1, wherein the step of performing acceleration slip regulation onthe four wheels respectively according to the road condition and therequired torque further comprises: controlling, when three wheels arelocated on a low adhesion road, the three wheels on the low adhesionroad to activate acceleration slip, and determing whether the vehiclespeed is less than a preset vehicle speed; controlling, when the vehiclespeed is less than the preset vehicle speed, a drive torque for a motorof a wheel on a high adhesion road to be the required torque; andperforming, when the vehicle speed is greater than or equal to thepreset vehicle speed, torque limiting on the motor of the wheel on thehigh adhesion road, so as to prevent the electric vehicle from lateraldisplacement, the drive torque for the motor of the wheel on the highadhesion road being equal to a sum of a drive torque for a motor of awheel, which is located on the low adhesion road and coaxial with thewheel on the high adhesion road, and a preset torque limit difference.9. An acceleration slip regulation device for a four-wheel driveelectric vehicle, comprising: a detection module, adapted to detectwheel speeds of four wheels of the electric vehicle and a depth ofdepression of an accelerator pedal; an estimation module, adapted toestimate a vehicle speed of the electric vehicle according to the wheelspeeds of the four wheels; a determination module, adapted to determinea road condition at a location of the electric vehicle according to thewheel speeds of the four wheels and the vehicle speed, the roadcondition comprising a low adhesion starting road, a joint road, and abisectional road; an acquisition module, adapted to acquire a requiredtorque of the electric vehicle according to the depth of depression ofthe accelerator pedal; and a control module, connected with thedetermination module and the acquisition module separately and adaptedto perform acceleration slip regulation on the four wheels respectivelyaccording to the road condition and the required torque.
 10. Theacceleration slip regulation device for a four-wheel drive electricvehicle according to claim 9, wherein the determination module isspecifically adapted to: determine whether the wheel speeds of the fourwheels are greater than the vehicle speed, respectively; determine, whenthe wheel speeds of the four wheels are all greater than the vehiclespeed, that the road condition is the low adhesion starting road;determine, when the wheel speeds of front wheels of the electric vehicleare both equal to the vehicle speed and the wheel speeds of rear wheelsare both greater than the vehicle speed, that the road condition is thejoint road and the electric vehicle enters a high adhesion road from alow adhesion road; determine, when the wheel speeds of the front wheelsare both greater than the vehicle speed and the wheel speeds of the rearwheels are both equal to the vehicle speed, that the road condition isthe joint road and the electric vehicle enters a low adhesion road froma high adhesion road; determine, when the wheel speed of only one wheelis greater than the vehicle speed and the wheel speeds of the otherthree wheels are all equal to the vehicle speed, that the road conditionis the bisectional road and the single wheel is located on a lowadhesion road; determine, when the wheel speed of one same-side wheel isgreater than the vehicle speed and the wheel speed of the othersame-side wheel is equal to the vehicle speed, that the road conditionis the bisectional road and one same-side wheel is located on a lowadhesion road; determine, when the wheel speed of one diagonal wheel isgreater than the vehicle speed and the wheel speed of the other diagonalwheel is equal to the vehicle speed, that the road condition is thebisectional road and one diagonal wheel is located on a low adhesionroad; and determine, when the wheel speeds of three wheels are greaterthan the vehicle speed and the wheel speed of the other wheel is equalto the vehicle speed, that the road condition is the bisectional roadand the three wheels are located on a low adhesion road.
 11. Theacceleration slip regulation device for a four-wheel drive electricvehicle according to claim 10, wherein the control module isspecifically adapted to: control, when the road condition is the lowadhesion starting road, the four wheels of the electric vehicle toactivate acceleration slip, each wheel being separately controlled by acorresponding motor.
 12. The acceleration slip regulation device for afour-wheel drive electric vehicle according to claim 10, wherein thecontrol module is further specifically adapted to: increase, when theelectric vehicle enters a high adhesion road from a low adhesion road,an integral coefficient in a PI controller corresponding to a motor of afront wheel respectively to increase an acceleration slip torque of themotor of the front wheel, and control the front wheel to exit theacceleration slip when the acceleration slip torque is greater than orequal to the required torque; and control, when the electric vehicleenters a low adhesion road from a high adhesion road, the front wheel toactivate the acceleration slip, and perform torque decrease on the motorof the front wheel to prevent the front wheel from slipping.
 13. Theacceleration slip regulation device for a four-wheel drive electricvehicle according to claim 10, wherein the control module is furtherspecifically adapted to: determine, when only one single wheel islocated on a low adhesion road, whether the vehicle speed is less than apreset vehicle speed; control, when the vehicle speed is less than thepreset vehicle speed, the wheel on the low adhesion road to activateacceleration slip; and perform, when the vehicle speed is greater thanor equal to the preset vehicle speed, torque limiting on a wheel on ahigh adhesion road, which is coaxial with the wheel on the low adhesionroad, so as to prevent the electric vehicle from lateral displacement, adrive torque for the motor of the wheel on the high adhesion road, whichis coaxial with the wheel on the low adhesion road, being equal to a sumof a drive torque for a motor of the wheel on the low adhesion road anda preset torque limit difference.
 14. The acceleration slip regulationdevice for a four-wheel drive electric vehicle according to claim 10,wherein the control module is further specifically adapted to: control,when one same-side wheel is located on a low adhesion road, the wheel onthe low adhesion road to activate acceleration slip, and perform torquelimiting on a wheel on a high adhesion road, so as to prevent theelectric vehicle from lateral displacement, a drive torque for the motorof the wheel on the high adhesion road being equal to a sum of acorresponding drive torque for a motor of the coaxial wheel on the lowadhesion road and a preset torque limit difference.
 15. The accelerationslip regulation device for a four-wheel drive electric vehicle accordingto claim 10, wherein the control module is further specifically adaptedto: control, when one diagonal wheel is located on a low adhesion road,the diagonal wheel on the low adhesion road to activate accelerationslip, and perform torque decrease on a motor of the diagonal wheel onthe low adhesion road.
 16. The acceleration slip regulation device for afour-wheel drive electric vehicle according to claim 10, wherein thecontrol module is further specifically adapted to: control, when threewheels are located on a low adhesion road, the three wheels on the lowadhesion road to activate acceleration slip, and determine whether thevehicle speed is less than a preset vehicle speed; control, when thevehicle speed is less than the preset vehicle speed, a drive torque fora motor of a wheel on a high adhesion road to be the required torque;and perform, when the vehicle speed is greater than or equal to thepreset vehicle speed, torque limiting on the motor of the wheel on thehigh adhesion road, so as to prevent the electric vehicle from lateraldisplacement, the drive torque for the motor of the wheel on the highadhesion road being equal to a sum of a drive torque for a motor of awheel, which is located on the low adhesion road and coaxial with thewheel on the high adhesion road, and a preset torque limit difference.